Pump control - Flygt

Engineering & Expertise
Operational optimization
Pump control

Engineering & Expertise
Total solution engineering
increases operational efficiency
Introduction
Determining the right control philosophy for
pump operation is a critical factor to ensure
the lowest life cycle cost of the entire pump
system. Proper management reduces the risk
of physical impediments, such as sedimentation,
clogging and floating debris, as well as
cuts energy costs and increases equipment
service life.
Engineering expertise is required in order to
realize energy, operation and maintenance
cost-savings through proper pump control. We
will provide guidance for the design of pump
control systems based on pump control theory
as well as years of experience from a number
of applications. Various control philosophies
are discussed in order to achieve an efficient
pump control.
Achieving lowest total cost of ownership
When providing pumping solutions, Flygt prefers to
take the total cost of ownership into consideration.
Unplanned
Investment
Operational
• Investment costs
Costs associated with design, excavation, civil work,
product purchases, installation and commissioning.
• Operational costs
Over time, energy usage and maintenance costs
are often the major contributors to the overall costs
along with the cost of labor required to run the
system.
• Unplanned costs
When things go wrong, such as pump failures stemming
from problematic station design, costs can
sky rocket. Unexpected downtime can cause sewer
backups, overflows, basement flooding and untreated
effluent. On top of that, you have to repair
pumps and take corrective measures regarding the
station design.
Theoretical analysis
Products
Physical tests
Engineering & Expertise
Thanks to our engineering expertise, we can lower
your total cost of ownership. We can analyze your
system using state-of-the-art computational programs.
We can test your pump station using scale
models if required. We can also provide you with
reference installations that are similar to your project.
All of this together with our premium products
provides you with an optimized design.
Reference installations
Engineering & Expertise
2

Introduction
Understanding the importance
of pump control
Poorly designed pump control systems can have adverse
effects on the entire pump system. This can
lead to the increased risk of sediment buildup in
pipes and sumps as well as clogging of the pumps.
Incorrect operating levels in the sump and velocities
in the pipes that are too high can significantly
increase energy consumption and costs. Equipment
lifetime may also be reduced due to transient effects
that result from high pressure at pump stops as well
as reduced pump motor lifetime due to starting and
stopping.
Flygt pump control
To optimize pump system operation, we take a
comprehensive approach to supplying complete
water and wastewater systems, including a broad
range of pump monitoring and control systems for
various pumping applications. These pump control
solutions are designed to deliver substantial energy
savings, by offering increased protection against
pump failure due to clogging and sedimentation,
lower maintenance costs and increased operational
efficiencies.
With our pump control philosophies, we offer different
levels of control and corresponding functions
through the Flygt pump control portfolio of
products. These levels range from local equipment
control to full control throughout the system and ultimately
to multi-site control of the entire plant. The
broad range of Flygt pump controls available within
the portfolio enables us to tailor a pump control solution
to meet the specific requirements of various
applications.
Application-specific products
Good pump station design takes into account all the individual
system components – including pumps, sump,
pipe installation and operating controls – as well as the
interaction among these. This ensures that all components
work in unison to deliver highly efficient operation
at the lowest possible total cost of ownership. As a
single reliable supplier, Flygt offers application-specific
products – from level switches to advanced SCADA
control systems – to ensure the most suitable type of
pump control for every application.
3

Pump control philosophies
Pump control affects
the entire system
Inlet
Challenges
When deciding upon control strategy the inlet
pipe’s vertical position must be taken into consideration.
If the inlet pipe is submerged during periods
of operation the fluid velocity will decrease and
there will be an increased risk for sedimentation.
On the other hand, when fluid levels in the sump
are too low, the static head will increase, thereby increasing
energy costs.
Pump control affects the operational efficiency of
the entire pump system – from the inlet, through
the sump and to the pump and the force main or
rising main. It is therefore important to understand
the interaction of all components with the pumped
fluid. Risk factors such as transients, clogging,
floating debris and sedimentation buildup must be
taken in account. Our pump control philosophies
solve the challenges related to each part of the
system by offering different levels of control and
corresponding functions selected from within the
Flygt portfolio of pump control products.
Solutions
To ensure the selection of the right start level, it
is important to understand the approach conditions
of the system prior to the station. The right
start level will prevent flooding in other parts of
the system, and reduce the energy consumption
related to the static head and number of operating
hours. Our expertise and experience ensure that
the right controller is selected to deliver reliable,
energy-efficient pump operation.
Non-submerged inlet.
Submerged inlet.
4

Pump
Challenges
Proper submergence of the pump inlet must be fulfilled
to prevent the risk of fully developed surface
vortices. Cavitation problems due to insufficient
available net positive suction head (NPSH) also have
to be avoided when choosing the stop level. These
phenomena can lead to vibrations and wear on
the pumps, shortening their lifetime. Stopping all
pumps at the same time should be avoided in large
systems with long force main pipes since this instigates
unnecessary pressure transients.
Solutions
For standard sump configurations, the recommended
minimum submergence requirements can
be found in “Design recommendation for pump
stations” for all Flygt pumps. It is also important to
ensure that the NPSH requirement is met.
In a multiple pump station, the pumps can be
stopped at sequential stop levels or with a time
delay between stops depending on the station conditions.
It is especially important with time delays between
the stops in large systems, in order to prevent
high immediate flow changes from developing into
pressure transients in the force main pipes. The Flygt
controllers have different built-in functions and can be
adapted to different types of systems, including multiple
pump installations.
Pumps with variable frequency drives
Pumps with variable frequency drives
Challenges
Pumps with variable frequency drives have an increased
risk of clogging in the pump due to the decreased
impeller speed during pump operation. The
decreasing impeller speed at ramp down also drastically
reduces the self-cleaning effect that occurs naturally
when back flushing, a phenomena that occurs
when the pump comes to a hard stop.
Solutions
To prevent clogging in pumps with variable frequency
drives, an impeller cleaning cycle is recommended.
Integrated logic enables monitoring of the pump for
signs of clogging. Upon detection of clogging, the
pump auto matically stops and begins to operate in reverse
rotation to remove the blockage. Pump cleaning
cycles are integrated into Flygt pump drives.
(Note: Pump cleaning cycles are not applicable on Flygt propeller pumps,
which are not designed for reverse rotation).
A clogged pump.
I Speed +
Illustration of the cleaning cycle.
5

Pump control philosophies
Sump
Challenges
To keep the sump clean it is crucial that everything
entering the sump is pumped away. Low flow regions
create stagnation zones in the sump where
bottom sediments and floating debris build up.
Solutions
Alternation
Automatic duty pump alternation is one method to
prevent stagnant zones in the sump. Alternation of
pumps implies equal running hours for all pumps
and reduces the number of start and stops per
hour. Alternation is also a good way to frequently
exercise all pumps installed. The alternation function
is built into Flygt pump controllers.
Sump cleaning cycles
Sump cleaning cycles are used to prevent odor
and the buildup of floating debris in the sump. It
is important to clean the sump on a regular basis.
Frequent cleaning cycles are recommended, where
the sump water level is pumped down below the
normal stop level until the pumps are snoring. All
floating debris will then be removed from the sump
by the pumps. Cleaning cycle functions are built
into Flygt pump controllers.
Active sump volume
The active sump volume is the volume between the
start and the stop level. When analyzing the active
sump volume, it is important to ensure that the volume
is sufficiently large enough to prevent the pumps from
starting too often. However, each time the pumps are
stopped they are backflushed, cleaning the pump
which is desirable. The active sump volume should
therefore be large enough to ensure that the pumps
do not start too often, but small enough to ensure that
the pumps are cleaned frequently.
Force main
The fluid velocity in the force main affects both the
degree of sedimentation and the energy consumption,
where the two are contradictive. At high velocities
the energy consumption increases but the
risk of sedimentation problems are low. In contrast,
when the velocity is low the energy consumption
will be low but the risk of sedimentation is increased.
Both the risk of sedimentation and energy
consumption should be considered when deciding
on control philosophies.
Sedimentation
problem
Energy consumption
Fluid velocity
Example of rugs and soft solids developing a surface mat.
When determining the optimal fluid velocity, it is important
to consider both sedimentation problems and energy
consumption.
6

Complete system
Challenges
In addition to the steady state pump duty analysis, it
is important to analyze the pump system with start
calculations and water hammer analysis. This will
ensure a sufficient starting torque, properly dimensioned
backup power supply, reliable pump duty
and protection against water hammer.
Solutions
Start calculations
Start calculations are recommended for large
pumps, and especially for propeller pumps due to
their torque characteristics. Start calculations will
indicate if there is sufficient torque margin between
the motor torque and the system load torque. The
calculations will also show if the motor is overloaded
during start. We design and manufacture our
own motors and have complete knowledge of their
motor characteristics, which implies very accurate
start calculations.
Duty analysis
To ensure sufficient NPSH, adequate rated motor
power and high pump efficiency, it is necessary to
conduct duty analysis. A duty analysis presents scenarios
where different pumps are running over the
system’s range of static heads, with various levels of
regulation and at varying speeds. This is important in
order to save energy and increase reliability. We have
developed our own tools to suit our pumps and applications
for basic and advanced duty analysis.
Water hammer analysis
To determine whether a system is susceptible to the
effects of water hammer, it is necessary to conduct
a water hammer analysis and, if required, to evaluate
the different methods of protection and select
and install the right methods. We can perform accurate
water hammer calculations, thanks to our extensive
testing of Flygt pumps and vast experience
with state-of-the-art mathematical modeling.
Water hammer analysis graphs from the Flygt Engineering Tool.
Start calculation graphs from the Flygt Engineering Tool.
7

Flygt pump control solutions
Optimizing pump
control systems
To provide the optimal solution for pump control
systems, it is necessary to take a total systems
engineering approach. We have the advanced
engineering software to assist with the conceptual
design of the control system, the practical
know-how and facilities for physical testing of the
control system as well as the engineering experience
and comprehensive portfolio of Flygt pump
control products.
Theoretical analysis
We develop our own engineering software, which
enables simulation of the pump system before it is
installed and commissioned. Simulation of the start
and stop of the system is critical from many perspectives,
such as pressure transients and sufficient motor
torque. With our knowledge and our tools, we can
help design reliable, energy-efficient systems. For
large custom designs or troubleshooting we perform
a computational fluid dynamics simulation study when
necessary to gain the complete picture of the flow
patterns inside the sump.
Premium products
We offer comprehensive solutions for pump control
based on our broad portfolio of Flygt pump control
hardware and software. Depending on the application,
our offerings range from standard setups
to programmable custom solutions and systems
for use in hazardous environments. These include,
but are not limited to, the following functions and
alarms:
• Alarm logs
• Start and running time counters
• High and low level alarms
• Power failure
• Personal alarms
• Pump capacity calculation
• Random start levels
• Dry run protection
• Constant level control
• Communication with SCADA, radio, ethernet cellular
systems and telephone lines
Physical testing
We have vast experience gained from testing
different control philosophies in a controlled environment
through small-scale model tests. When
designing large custom stations, it may be necessary
to conduct specific small-scale model tests to
analyze the control philosophy and ensure that no
adverse hydraulic issues arise.
8

Reference installations
Proven worldwide
Flygt has applied our pump control philosophies
together with our premium products on thousands
of installations around the world. Engineering expertise
and years of experience have resulted in the
success of these installations. Two such cases are
described below.
Sweden: Pump station
Challenge
Eighteen Flygt pump stations transport wastewater at
a popular recreational and amusement area in central
Stockholm. One of the pump stations handles restaurant
wastewater containing fats, oils and grease.
The liquefied oil and grease in high-temperature
dishwashing water solidifies after transportation to
the pump station. This caused severe odor problems
and grease build-up on the pump station walls, sump
water surface, Flygt CP3102 pumps, guide bars, level
sensor and other pump station equipment, increasing
the risk of failure in the station. Expensive maintenance
procedures had to be carried out every two to
three months in order to remove accumulated sludge
and clear the station of greasy buildup.
Solution
Our engineers recommended the installation of a
Flygt APF cleaning function through an electronic
device for automatic pump sump cleaning. The controller
automatically initiates pump operation in order
to drain sump water to the lowest possible level,
thereby removing grease and dirt laying on the surface
of the water. This enables the pump station to
operate for a significantly longer time without requiring
any sludge removal.
United Kingdom: More energy-efficient pump station
Challenge
Four high-efficiency 100 kW Flygt N-pumps operating
with variable frequency drives (VFDs) deliver
a total volume of 0.8 m 3 /s (12,700 US gpm) and
consume 1,000,000 kWh of energy per year. The
customer wanted to reduce energy costs but maintain
reliable, trouble-free operation without the
problems of clogging, sedimentation and floating
debris.
Solution
We performed an energy audit by measuring flow,
head, power and analyzing the control philosophy.
By analyzing the results from the measurements,
we identified that adjustment of the settings on the
VFDs would lead to more energy-efficient operations.
Estimated energy savings amounted to between
five and 15 percent.
9

Services AND support
Engineering & Expertise
To ensure reliable and highly efficient operation,
we offer comprehensive support and service for
pump station design, system analysis, installation,
commissioning, operation and maintenance.
Design tools
When you design pump stations, we can offer
advanced engineering tools to generate sump
designs. Our design recommendations give you
essential information regarding dimensions and
layout. In short, we assist you every step of the
way to make sure you optimize performance and
achieve energy-efficient operations.
Theoretical analysis
Computational fluid dynamics (CFD) can provide far
more detailed information about the flow field in a
fraction of the time required to get the same information
through physical hydraulic scale model testing.
Using CFD in combination with computer-aided
design (CAD) tools, it is possible to obtain a more
efficient method of numerical simulation for pump
station design.
To obtain a reliable, energy-efficient pumping
system, it is important to analyze all modes of operation.
To analyze the transient effects at pump
start and stop with respect to flow and head as
well as the electrical parameters such as current
and torque, it is also important to have an accurate
mathematical description of the pump and motor,
which is gained, in part, from extensive testing in
our laboratories.
10

Physical testing
Physical hydraulic scale model testing can provide
reliable, cost-effective solutions to complex hydraulic
problems. This is particularly true for pump stations
in which the geometry departs from recommended
standards or where no prior experience with the
application exists. Scale model testing can also be
employed to identify solutions for existing installations
and has proven to be a far less expensive way
to determine the viability of possible solutions than
through trial and error at full scale.
Reference installations
We have conducted system analysis and designed
pump stations for thousands of installations around
the world. Engineering expertise and years of experience
gained from the design and operation of these
installations have been a critical success factor when
analyzing, testing and commissioning new pump
installations.
When our standard design recommendations are
not met, we can assist in determining the need for
physical testing as well as planning and arranging
the testing and evaluating the results.
Theoretical analysis
Products
Physical tests
Reference installations
Engineering & Expertise
Model test photos courtesy of Hydrotec Consultants Ltd.
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1203 . Operational optimization . 1 . Master . 1 . 20120419
For more information on how Xylem can help you, go to xyleminc.com.
Flygt is a brand of Xylem. For the latest
version of this document and more
information about Flygt products visit
www.flygt.com